Skip to main content

NSA Snoop and Error Proof Your Archives

An Englishman's Home is His Castle:

In 1760, William Pitt (the Elder) made a famous declaration of this right. "The poorest man may in his cottage bid defiance to all the force of the Crown.  It may be frail, its roof may shake, the wind may blow through it. The rain may enter. The storms may enter.  But the king of England may not enter.  All his forces dare not cross the threshold of the ruined tenement."

There is many a ruined castle in Europe.  You need to defend your castle if you want it to keep its value!

You should also consider the problem of data corruption, since any single bit error in an encrypted archive, will render the whole thing unreadable.

Also remember this: Always tar a directory, never tar a bunch of files. 

 It is extremely annoying when you get an archive from someone, untar it and end up with a million files scattered throughout your home directory...


Encrypting an Archive with GPG

An easy way to secure your data against unwarranted NSA and GCHQ snoops is with gpg.  Always use gpg before uploading archives to a public file server such as DropBox, Copy or Evernote.

Using pipes, you can string the tape archiver tar, bzip2 and gpg together like this:
$ tar -cj test | gpg -c >test.tar.bz2.gpg

(or use gpg -er username for key based encryption)

and to reverse it:

$ gpg -d < test.tar.bz2.gpg | tar -xj

The key configuration of GPG is shown in another post. 

 

Forward Error Correction

A good way to protect your data against corruption is with a Reed Solomon forward error correcting code - it is used on CDROMs.  There is a little known utility available that does it, called rsbep by Guido Fiala and you can get the source using this link: http://www.filewatcher.com/_/?q=rsbep

Then build it the usual way with ./configure; make; sudo make install.  It is part of the BSD and Debian distributions.

Using pipes, you can string the tape archiver tar, bzip2, rsbep and gpg together like this:

$ tar -cj test | gpg -c | rsbep >test.tar.bz2.gpg.rs

(or use gpg -er username for key based encryption)

and to reverse it:

$ rsbep -d < test.tar.bz2.gpg.rs | gpg -d | tar -xj

The Reed Solomon code will protect your archive against error bursts and will help to ensure that you can read the data back from a failing archive system, many years later.

 

Parity Bits

There is also a utility called par2 (and the handy GUI PyPar2) which adds Reed Solomon parity bits in a series of separate files.  These are in the par2cmdline and pypar2 packages.  This can be used to protect any files, but when you copy things around, you got to remember to pass the parity data along too.

Preventive Measures Using Par2

In order to ensure that I get into and stay in the habit of using gpg, I created a couple of scripts, so I can simply do:

$ targpg directory
and
$ untargpg directory

and the scripts will handle the messy details.

I tested the error recovery by corrupting the archive with hexedit - it works like magic!

Make an archive script like this called /usr/local/bin/targpg:
#! /bin/bash
echo Make an encrypted archive of a directory
tar -cj "$1" | gpg -c >"$1.tar.bz2.gpg"
md5sum "$1.tar.bz2.gpg" > " $1.tar.bz2.gpg.md5"
parcreate -n1 "$1.tar.bz2.gpg"
ls -al "$1"*

as well as untargpg:
#! /bin/bash
echo Untar a GPG encrypted archive $1
RESULT=$(md5sum -c "$1.tar.bz2.gpg.md5")

if [ "$RESULT" != "$1.tar.bz2.gpg: OK" ]
then
  echo MD5 error - Attempt a repair
  par2repair $1.tar.bz2.gpg.par2
fi

# Try to decrypt and untar regardless   
# because the md5 and par2 files may be missing
gpg -d < "$1.tar.bz2.gpg" | tar -xj
ls -al "$1"*
 

and then one day when your disk goes south, par2repair may save the day.

La voila!
Labels:

Comments

Post a Comment

On topic comments are welcome. Junk will be deleted.

Popular posts from this blog

OpenEMS with Octave and SciLAB

I wanted to do some advanced RF antenna development work and needed an electromagnetic field solver that is a bit more up to date than NEC2 .  Commercial solvers from Matlab , Ansys and others are hideously expensive (in the order of $20,000 to $50,000) and do not fit in the wallet of a hobbyist or a small consulting company.  Recently, openEMS became available and it fills the niche with a capable free tool.  In general, openEMS is a solver - a Finite-Difference Time-Domain (FDTD) numerical engine.  You interact with it through Octave , which is almost identical to Matlab .  You can watch a good video by Thorsten Liebig here: https://www.youtube.com/watch?app=desktop&v=ThMLf0d5gaE   Getting it to work is a little painful, but it is free, so bear with it - then save a backup clone, or a zipped copy of the whole virtual machine directory and NEVER update it, to ensure that it keeps going and doesn't get broken by future updates, right when you are ...
Post a Comment
Read more

Parasitic Quadrifilar Helical Antenna

This article was reprinted in OSCAR News, March 2018:  http://www.amsat-uk.org If you want to receive Satellite Weather Pictures , then you need a decent antenna, otherwise you will receive more noise than picture. For polar orbit satellites, one needs an antenna with a mushroom shaped radiation pattern .  It needs to have strong gain towards the horizon where the satellites are distant, less gain upwards where they are close and as little as possible downwards, which would be wasted and a source of noise.  Most satellites are spin stabilized and therefore the antenna also needs circular polarization, otherwise the received signal will flutter as the antennas rotate through nulls. The helical antenna, first proposed by Kraus in 1948, is the natural solution to circular polarized satellite communications.  It is a simple twisted wire - there seems to be nothing to it.  Various papers have been published on helix antennas, so the operation is pretty well ...
3 comments
Read more

Yagi Antenna for 900 MHz ISM Band

I like tinkering with wire antenna designs, since they are simple and cheap to make.  Mr Yagi invented his antenna about 100 years ago, but there are still some things left to learn about it. 900 MHz ISM Band Yagi The 900 MHz ISM band ranges from 902 to 928 MHz.  Covering the whole band with a single Yagi antenna is difficult, since they are inherently narrow band devices.  Consequently some tweaking is required and the result below is a desensitized design that can be built and replicated quite easily, but you need a network analyzer - "To Measure, is to Know!" A Yagi generally consists of a Reflector, Radiator and one or more Director elements, arranged on a boom.  For a small Yagi, a wooden ruler works a treat, since one can easily mark the position of the wires.  The wire elements are fastened to the bottom of the ruler with hot glue.  The wire elements are  made from straightened out jumbo size paper clips.  The balun, is tw...
Post a Comment
Read more